Stoichiometry of biological nitrogen transformations in wetlands and other ecosystems.

The stoichiometric equations of ammonification, nitrification and denitrification have demonstrated that the nitrogen cycle in nature is rather complicated. The mechanisms of biological nitrogen transformations are very important for analysis, design, operation and optimal control of natural ecosystems or engineered systems for nitrogen removal, and accurate stoichiometric equations can help in the maintenance of these environments. In this study, the new stoichiometric equations of intermediate nitrification, and heterotrophic and autotrophic denitrification with sulfur as the electron donor have been developed and discussed. The parameter values of f(s) (the fraction of electron donor coupled to cell synthesis) in stoichiometric equations of nitrification and denitrification are calculated according to experimental results implied in previously reported stoichiometric equations. Some new stoichiometric relationships of nitrification and denitrification, such as the O(2) demand for nitrifications, chemical oxygen demand/N ratios and the yield coefficients for denitrifications have been established. The pathway steps of nitrification and denitrification have been discussed.